Speed control apparatus

ABSTRACT

An arrangement for controlling the surface speed of one endless xerographic plate relative to another in a duplex xerographic machine. According to the arrangement, an endless member along a first portion thereof is operatively associated with one of the xerographic plates to be driven at a surface speed proportional to the respectively associated xerographic plate and along a second portion thereof is operatively associated with the other of the xerographic plates to be driven at a surface speed proportional to the other of the respectively associated xerographic plates. The endless member along a third portion thereof is formed into a loop, the size of which may vary according to variations in the relative surface speeds between the xerographic plates. Upon detection in variations in the size of the loop portions of the endless member, the surface speed of the respective xerographic plates may be operatively varied to maintain equal surface speeds between each of the xerographic plates.

[ 1 Sept. 26, 1972 United States Patent- Ticknor SPEED CONTROL APPARATUS [72] Inventor:

Primary Examiner-Bernard A. Gilheany Assistant Examiner-W. E. Duncanson, Jr.

Raymond G. Tlcknor, Fairport, NY.

[73] Assignee: Xerox Attorney-Paul M. Enlow, James J. Ralabate, Donald 'F. Daley and Terry J. Anderson Corporation, Stamford, Conn.

[22] Filed: May 1,1970

21 Appl. No.: 33,566

g to the arrangement, an endless member along a first portion thereof is operatively associated with one of the xerographic plates to be driven at a surface speed proportional to the respectively associated xerographic plate and along a second portion thereof is operatively as- [58] Field of 18/6, 7, 45, 68

sociated with the other of the xerographic plates to be References Cited UNlTED STATES PATENTS driven at a surface speed proportional to the other of the respectively associated xerographic plates. The endless member along a third portion thereof is 876 12/1947 Formhals et a1" 318/6 ing to variations n the relative surface speeds between 764 6/1963 C 6 the xerographic plates. Upon detection in variations m 825 4 96 l the size of-the loop portions of the endless member, 158 1 the surface speed of the respective xerographic plates I Ca may be operatively varied to maintain equal surface speeds between each of the xerographic plates.

) a a 7 t a 9 a 9 a 9 r 8 Claims, 5 Drawing Figures I 1 SPEED CONTROL APPARATUS BACKGROUND OF THE INVENTION This invention relates generally to an arrangement for controlling the speed of one moving surface relative to another and more particularly to an arrangement for controlling the surface speed of one endless xerographic plate relative to anotherin a duplex xerographic machine.

In the art of xerography or electrophotography the desirability of printing on both sides of a copy sheet has long been recognized. However, notwithstanding the desirability of such duplex. xerographic printing or copying, numerous obstacles have been encountered in the implementation of duplex copying. For example, the fusing step of xerography as conventionally performed utilizing heat or solvent vapor has caused the powder image to become soft and tackified whichin turn has presented a problem of offsetting and smudging. of the image areas. This has been especially true in single pass duplexing wherein images are placed on opposite sides of the sheetessentially simultaneously and then simultaneously'fused. Where sequential transfer has been involved or dual pass duplexing, complicated scheduling has been required for subsequent interspersing of the various pages.- Furthermore, inasmuch as heat fusing, 1 the most desirable fusing method, can cause crinkling as well as drying of the copy sheet such that it is difficult to get uniform contact for a subsequent electrostatic transfer step the dual pass approach has been less desirable than the single pass approach in duplexing.

The single pass approach to duplexing has itself not been without major obstacles in obtaining a workable arrangement. For example, many problems have resulted in trying to produce simultaneous or essentially simultaneous transfer of the unfused xerographic images to the copy sheet without in some way interferring with the quality of the image, or damaging the somewhat delicate xerographic plate. Because of the nature of the xerographic'process it has therefore been found desirable in single pass duplexing to utilize two xerographic plates which are not only spaced on either side of the copy sheet or copy material but are also spaced from each other in the direction of copy sheet travel. In such an arrangement, instead of producing simultaneous transfer of the xerographic images to the copy sheet the images are actually transferred to the support material at different points along the copy sheet path but yet occur close enough in proximity to each other to be considered essentially simultaneous transfer.

However, even in single pass duplexing utilizing essentially simultaneous transfer, the surface speeds at which each of the xerographic plates is driven relative to each other and the support material can have an adverse affect on the image quality if not accurately controlled. It is therefore extremely desirable to drive each of the xerographic plates at the same surface speed relative to each other and also the same surface speed relative to the speed at which the copy material is advanced.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention It is another object of the present invention to provide an arrangement by which the surface speed of one xerographic plate may be controlled relative to another in a duplex xerographic machine.

It is still another object of the present invention to provide an-arrangement for sensing a speed change between two moving xerographic plates in a duplex xerographic machine.

It is still a further object of the present invention to prevent smearing and smudging of the unfused xerographic images in a single pass duplexing machine by accurately controlling the speed at which the xerographic plates are driven.

It is yet a further object of the present invention to provide an arrangement for positively controlling the speed at which one xerographic plate is driven relative to another in a xerographic duplexing machine as a copy material passes over a portion of the periphery of each of the xerographic plates for transfer of xerographic images on each of the xerographic plates to the copy material.

These and other objects of the present invention are obtained by means of an endless member having a first portion thereof operatively associated with one of the xerographic plates in a xerographic duplexing machine to be driven at a speed proportional to the respectively associated xerographic plate and a second portion thereof operatively associated with another of the xerographic plates in a xerographic duplexing machine to be driven at a speed proportional to the respectively associated xerographic plate. The endless member at a third portion therealong is formed into a loop, the length of which at any particular time period is dependent upon the speed at which the respective xerographic plates are being driven.

A sensing arrangement operatively associated with the loop portion of the endless member senses variations in length of the loop portion to responsively produce a corresponding change in the speed of at least one of the xerographic plates.

Other objects of the invention will become readily apparent to those skilled in the art in view of the following detailed disclosure and description thereof, especially when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a xerographic duplexing arrangement in which the speed control arrangement as contemplated by the present invention is particularly adapted for use.

FIG. 2 is a perspective view of an alternate xerographic duplexing arrangement in which the speed control arrangement as contemplated by the present invention is particularly adapted for use.

FIG. 3 is an enlarged perspective view showing the loop arrangement of FIGS. 1 and 2.

FIG. 4 is a partly schematic diagram showing one embodiment of loop sensing arrangement as contemplated by the present invention.

FIG. 5 is a diagram showing the manner in which the relative speed between two xerographic plates may be controlled through the sensing arrangement of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1 of the drawings, there is illustrated a single pass xerographic duplexing arrangement in which the speed control arrangement as contemplated by the present invention is particularly adapted for use. As illustrated therein, a pair of xerographic drums or cylinders 2 and having suitable photoconductive surfaces 4 and 7 respectively coated thereon are mounted for rotation in a xerographic machine on shafts 3 and 6 respectively. Although the various aspects pertaining to the xerographic process have been omitted from the drawings for clarity it is to be understood that each of the xerographic plates 4 and 7 may be imaged according to the xerographic technique. To this end each of the xerographic plates comprising a layer of photoconductive material on a conductive backing is given a uniform electrostatic charge on the surface thereof and then exposed to the subject matter to be reproduced. The exposure discharges portions of the surface in accordance with the light pattern of the original image thereby leaving a latent electrostatic image of the original on or in the surface. The latent electrostatic image is then made visible by development with developers which may comprise in general a mixture of suitable pigmented, or

charging in a manner well known and advanced by web drive means from a web supply roll to a web take-up roll.

An endless member 8 which may comprise an endless flexible tape or belt member is operatively associated along a first portion'thereof with one of the xerographic drums to be driven at a speed proportional to the speed at which that particular xerographic drum is driven. Endless tape or belt member 8 is also operatively associated along a second portion thereof with the other of the xerographic drums to be driven at a speed proportional to the speed at which the other xerographic drum is driven. Thus according to the ardyed resin based powders referred to as toners. During development, the toner is brought into contact with the electrostatic latent image which attracts the toner to the photoconductor in those areas representative of the original image. Thereafter the developed images are transferred to the copy support material which may be conveniently in the form of a web of paper stock 1 by contacting the image areas with the web and applying a uniform electrostatic charge to the web of a polarity opposite to that of the toner images. In the arrangement as shown in FIG. 1, web stock 1 passes between drums 2 and 5 respectively so asto have one side of the web 1 in contact with the photoconductive surface 4 and the other side of the web 1 in contact with the photoconductive surface 7. xerographic drums 2 and 5 are also slightly spaced from each other in the direction of web travel so that instead of producing simultaneous transfer of the images from the xerographic drums 2 and 5, transfer is accomplished to one side of the web slightly ahead in point of time from the other, resulting in essentially simultaneous transfer. The spacing of the respective xerographic drums from each other in the direction of web travel is done for convenience in arranging the various components for effecting the xerographic process and in no way affects the speed control arrangement as contemplated by the present invention. The speed control arrangement according to the present invention is equally adaptable to systems incorporating transfer of both of the images to the web simultaneously as well as systems which utilize essentially simultaneous transfer as described in connection with FIGS. 1 and 2.

xerographic drums 2 and 5 are rotated about shafts 3 and 6 respectively in the direction of the arrows by means of drive motors MOT-1 and MOT-2 operatively connected to the respective drum shafts. Web material 1 may be conveniently electrostatically tacked to the respective drums at the transfer station by corona rangement shown in FIG. 1, endless tape 8 along a first portion thereof is entrained about a portion of the periphery of xerographic drum 2 to be driven along that portion at a surface speed equal to the surface speed at which drum 2 is driven. Similarly endless tape 8 along a second portion thereof is entrained about a portion of the periphery of xerographic drum 5 to be driven along that portion at a surface speed equal to the surface speed at which drum 5 is driven. In the preferred arrangement, means are provided such as sprocket teeth on drum members 2 and 5 which mate with apertures in endless member 8 to provide a positive drive arrangement of endless member 8 over drum members 2 and 5. r

As may be seen from FIGS. 1 and 3, endless member 8 along a third portion thereof is formed into a loop. The loop portion of endless member 8 is generated by passing endless member 8 over a pair of fixed rollers or pulley members 15 and 16 and a moveable pulley or roller member 14 which is displaceable in a direction into or out of the loop formed in the third portion. Pulley members 15 and 16 are operatively mounted for rotation on a support 11 which in turn is secured at a suitable location relative to drum members 2 and 5. Moveable pulley or roller member 14 may be supported through a slot in plate 11 by means of flange 9 to permit movement of pulley member 14 in a direction both into and out of the loop. A biasing means may optionally be provided such as spring member 21 shown in FIG. 4 to normally bias pulley member 14 in a direction into the loop.

Thus, it will be appreciated that as drum members 2 and 5 are driven by the respective drive arrangements, the associated portions of endless member 8 in contact with, drum members 2 and 5 will be positively driven at the same surface speed as the respective drum members. It will also be appreciated that when the surface speed of each of the drums 2 and 5 is equal, the size of the loop portion of endless member 8 will remain constant. Similarly, when the surface speed of each of the drums 2 and 5 is equal, the position of roller member 14 in the slot of plate 11 will remain constant. However, in the event that a change in either of the drum speeds occurs, the size of the loop in endless member 8 will change accordingly and the positioning of roller member 14 relative to the slot in plate 11 will be altered. Thus, sensing means may be utilized to sense the positioning of roller member 14 and hence detect any change in the speed of the drum members. Upon detection of any such change, the drive to at least one of the drum members may be operatively controlled to supply a correction to-the drum speed thus compensating for the detected deviation.

FIG. 2 illustrates a slightly different arrangement by which, the xerographic images are formed. According to this arrangement, a first cylindrical member 2' is mounted for rotation within the xerographic machine by means of shaft 3'. A photoconductive material 4' which may be conveniently in the form of an endless belt member or alternatively in the form of a length of' web material passes about cylindrical member 2'. to present images on the photoconductive member 4' proximate to web material 1 to which the images are to be transferred. A second cylindrical member 5' is mounted for rotation within the xerographic machine by means of shaft 6'. A photoconductive member 7" which may be conveniently in the form of an endless I belt or alternatively in the form of a length of web material passes over a portion of cylindrical member 5 to present images on photoconductive member 7 proximate to web material 1' to which the images are to be transferred. It will be appreciated that as in the case of the embodiment illustrated in-FIG. l, the cylindrical members 2' and 5 are respectively spaced from each other in the direction of web travel so that instead of producing simultaneous transfer of the images from the photoconductive surfaces 4' and 7' respectively,

transfer is accomplishedto one side of the web material 1' slightly ahead in point of time from the other, resulting in essentially simultaneous transfer; Again, the

spacing of the respective cylindrical members 2' and S from each other in the direction of web travel is done for convenience in arranging the various components for effecting the xerographic process and in no way affects the speed control arrangement as contemplated by the'present invention.

Cylindrical members 2' and 5 are rotated about shafts 3" and 6' respectively in the direction of the arrows by means of drive motors MOT-l and MOT-2 operatively connected to shafts 3 and 6 respectively. As inthe embodiment described in connection with FIG. 1, web material 1' may be conveniently electrostatically tacked to the respective surfaces of photoconductive members 4' and 7 at the transfer station by corona charging in a manner well known. The web material 1' may be advanced by means of a web drive mechanism from a web supply roll to a web takeup roll.

A first pulley member 12 is operatively connected to cylindrical member 2' on shaft 3 to be driven at a speed proportional to the speed at which cylindrical member 2 is driven and accordingly, a speed proportional to the speed at which photoconductive surface 4 is driven. A second" pulley member 13 is operatively connected to cylindrical member 5' on shaft 6' to be driven at a speed proportional to the speed at which cylindrical member 5f and the speed at which photoconductive member 7- is driven. The size of pulley members 12 and 13 may'optionally be chosen so as to provide a surface speed along the peripheral portions thereof either equal to the surface speeds of the respective photoconductive members 4' and 7 or altematively a diameter which produces a surface speed thereon less than thesurface speeds of the photoconductors 4 and 7' but proportional thereto.

An endless member 8 as in the case of the embodiment described in connection with FIG. 1, may comprise an endless flexible tape or belt member which is operatively associated along a first portion thereof with one of the pulley members '12 or 13 to be driven at a speed proportional to thespeed at which one of the photoconductive members is driven. Endless tape or belt member 8'ais also operatively associated along a second portion thereof withthe other of the pulley members 12 or 13 to be driven at a'speed proportional to the speed at which the other of the photoconductive members is driven. Thus, according to the arrangement shown in FIG. 2 endless tape 8' along a first portion thereof is entrained about a portion of the periphery of pulley member 12 to be driven along that portion at a surface speed proportional to the surface speed at which photoconductivemernber 4' is driven. Similarly,

endless tape member 8' along a second portion thereof is entrained about a portion of the periphery of pulley member 13 to be driven along that portion at a surface speed proportional to the surface. speed at which photoconductive member 7' is driven. Again as in the embodiment of FIG. 1, means such as sprocket teeth are provided on pulley members 12 and 13 which mate with apertures in endless member 8' to provide a'positive drive arrangement of endless member 8' over pulley members 12 and 13.

As may be seen from FIGS. 2 and 3, endless member 8 along the third portion thereof is formed into aloop. v

.Moveable pulley or roller member l4 is supported through a slot in plate 11 by means of flange 9 to permit movement of pulley member 14 in a direction both into and out of the loop. A biasing means may optionally be provided such as spring member 21 shown in FIG. 4 to normally bias pulley member 14 in a direction into the v loop.

Thus, as in the embodiment described in connection with FIG. 1, it will be appreciated that as cylindrical members 2' and 5' are driven by the respective drive arrangements, photo-conductive members 4 and 7' will be respectively driven about the surfaces of cylindrical members 2 and 5 As cylindrical members 2' and 5 are thus driven, the associated portions of endless member 8 in contact with pulley members 12 and 13 respectively will be driven at a surface speed proportional to the surface speed at which the respectively associated photoconductive members 4 and 7' are driven. It will also be appreciated that when the surface speed of each of the photoconductive members 4' and 7' is equal, the size of the loop portion of endless member 8' will remain constant. Similarly, when the surface speed of each of the photoconductors 4' and 7' is equal, the position of roller member 14 in the slot of plate 11 will remain constant. However, in the event that a change in either of the drum speeds occurs, the size of the loop in endless member 8 will change accordingly and the positioning of roller member 14 relative to the slot in plate 1 1 will be altered. Thus, sensing means may be utilized as in the embodiment described in connection with FIG. 1 to sense the positioning of roller member 14 and hence detect any change in the speed of the vphotoconductive members. Upon detection of any such change, the drive to at least one of the cylindrical members driving the respectively associated photoconductive members may be operatively controlled to supply a correction to the speed of the cylindrical members thus compensating for the detected deviation.

Various arrangements may be employed for detecting deviations in the size of the loop portion of endless member 8. One arrangement which may be utilized to detect deviations in the size of the loop portion formed in endless member 8 is that as illustrated in connection with FIG. 3. Asshown therein, a light source designated LMP-l is-positioned on one side of pulley member 14 and a cooperatively arranged photosensitive device such as photocell PC-l is positioned on the other side of pulley member 14 opposite light source LMP-l. Light source'LMP-l and photocell PC-l are optically aligned with pulley member 14 such that when, pulley member 14 resides at a predetermined location along the slot in plate 11, light from the light source LMP- l will pass through an opening 10 located centrally of pulley member 14 to permit light rays from thelight source LMP1 to impinge upon the photosensitive surface of photocell PC-l. In this condition, the length of the loop portion in endless member 8 would be of a constant predetermined length indicating that each of the photoreceptors is being driven at the same surface speed. However, upon any deviation in the surface speed of one of the photoreceptors, pulley member 14 will be displaced within the slot of plate 11 to a point whereat light from light source LMP-l will no longer be permitted to impinge upon the photosensitive surface of photocell PC-l. In this condition, a suitable electrical control signal will be generated by photocell PC-l to operatively control the drive input to at least one of the photoconductive surfaces to correct the relative surface speed between which the respective photoconductive members are driven. Various logical electrical schemes for accomplishing this result are well known and a detailed description thereof is not deemed necessary for a complete understanding of the invention.

drive mechanisms of at least one of the photoconductive members.

As may be seen from FIG. 5, cylindrical member 2 may be driven through a direct drive arrangement from synchronous drive motor MOT-1. As may also be seen from FIG. 5, cylindrical member 5 may be driven through a differential drive arrangement 17 operatively connected to synchronous drive motor MOT-2. Cylindrical member 5 may also be driven by means of a reversible DC drive motor MOT-3 operatively con- A preferred arrangement for sensing deviations in the size of the loop portion of endless member 8 and for correcting the speed at which the photoreceptors are driven is illustrated in connection with FIGS. 4 and 5. As may be seenfrom FIG. 4, pulley member 14 is normally biased in a direction into the loop or downwardly as seen in FIG. 4 by means of a spring member 21. A light source LMP-l is positioned at one side of pulley member 14 in optical alignment therewith so as to permit light rays from light source LMP-l to pass through aperture 10 in pulley member 14. A reflective member 22 having a convexly curved reflecting surface thereon is positioned on the side of pulley member 14 opposite to the location of light source LMP-l in a position to receive light passing through aperture 10 in pulley member 14 on the convexly curved reflecting surface. A pair of lens members 19 and 20 are operatively as sociated with pulley member 14 on opposite sides thereof to provide an optical level from light source LMP- l focused upon the reflecting surface of reflective member 22. v

nected to a second input to the differential drive arrangement 17. Reversible DC drive motor MOT-3 is operatively connected to a DC power supply 18 which is operatively controlled by. means of the photo relay tubes PR-l, PR-2, PR-3 and PR-4.

As will be apparent from the schematic illustrationof FIG. 5, one group of photo relay tubes such as PR-l and PR-2 will be utilized to drive reversible DC drive. motor in one direction and a second group of the photo relay tubes such as PR-3 and PR-4 will be utilized to drive DC reversible drive motor MOT-3 in a second direction of rotation. As drive motor MOT-3 is thus driven, a correctional driving force through differential input 17 will be made to cylindrical member 5 thus supplying a correctional drive input to the cylindrical member 5 to alter the surface speed at which the photoconductive surface associated with cylindrical member 5 is driven. Through this arrangement the relative surface speeds between the photoreceptive surfaces associated with cylindrical members 2 and 5 can be maintained equal.

From the foregoing description it will therefore be appreciated and understood that there has been provided an arrangement for controlling the surface speed of one endless xerographic plate relative to another in a duplex xerographic machine.

While the invention has been described with reference to preferred arrangements, it will be generally understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention.

What is claimed is: a

1. Apparatus for controlling the surface speed of one endless xerographic plate relative to another in a duplex xerographic machine comprising,

an endless flexible member,

means defining a closed path of travel along which a said endless member is driven including means along a first portion thereof operatively associated with one of said xerographic plates for driving an associated portion of said endless member at a speed proportional to the speed at which said xerographic plate is driven, means along a second portion thereof operatively associated with the other of said xerographic plates for driving an associated portion of said endless member at a speed proportional to the speed at which said other xerographic plate is driven, and means along a third portion thereof for forming a loop in said endless member, means'for sensing variations in the size of the loop of said endless member along the third portion of said path of travel including, a light source positioned at one side of said loop, a reflecting member positioned at the side of said loop opposite said light source in' optical alignment therewith to receive radiation from said light source, and a plurality of photosensitive devices disposed from said reflecting member in optical alignment therewith to receive radiation from said light source at predetermined lengths of said loop, and drive means operatively associated with atleast one of said xerographic plates and said plurality of photosensitivedeviees for controlling the speed at which at least one of said xerographic plates is driven.

2. Apparatus for controlling the surface speed of one I said endless member having a second portion thereof operatively associated with another of said moving surfaces, to be driven at a speed proportional to said other of said moving surfaces,

said endless member having a third portion thereof formed into a loop, the length of which at any particular time period is dependent upon the relative speed at which said surfaces are moving,

means operatively associated with the loop portion of said endless member for sensing variations in the length of said loop and for producing a corresponding change in the speed of at least one of said moving surfaces, said sensing means includa light source positioned at one side of said loop,

a reflecting member positioned at the side of said loop opposite said light source in optical alignment therewith to receive radiation from said light source, and

a plurality of photosensitive devices disposed from said reflecting member in optical alignment therewith toreceive radiation from said light source at predetermined lengths of said loop.

endless xerographic pla'te relative to another in a duplex xerographic machine comprising,

an endless flexible member having a first portion 4. Apparatus for controlling the speed of one moving surface relative to another comprising,

thereof operatively associated with one of said xerographic plates to be driven at a surface speed proportional to that of said xerographic plate and a second portion thereof operatively associated with another of the xerographic plates to be driven at a surface speed proportional to that of said other xerographic platje,

means for forming a loop in said endless member along a third portion thereof between the as sociated'portions of said xerographic plates, said loop being of a predetermined length when the surface speed at which one of the xerographic plates is driven is at a predetermined level relative to the surface speed at which the other of the xerographic plates is driven,

means for sensing variations in the size of said loop from said predetermined length including a light source positioned at one side of said loop, a reflecting member positioned at the side of said loop opposite said light source in optical alignment therewith to receive radiation from said light source, and a plurality of photosensitive devices disposed from said reflecting member in optical alignment therewith to receive radiation from said light source at predetermined lengths of said loop,

and

drive means operatively associated with at least one of said xerographic plates and said plurality of photosensitive devices for producing a correctional change in the relative speed at which at least one of said xerographic plates is driven in response to a variation in the size of said loop from said predetermined length.

3. Apparatus for controlling the speed of one moving surface relative to another comprising,

an endless member having a first portion thereof operatively associated with one of said moving surfaces, to be driven at a speed proportional to said one of said moving surfaces,

an endless flexible member,

means defining a closed path of travel along which said endless member is driven including means along a first portion thereof operatively associated with one of said moving surfaces for driving an associated portion of said endless member at a speed proportional to the speed at which said moving surface is driven, means along a second portion thereof operatively associated with the other of said moving surfaces for driving an associated portion of said endless member at a speed proportional to the speed at which said other moving surface is driven, and means along a third portion thereof for forming a loop in said endless member,

means for sensing variations in the size of the loop of said endless member along the third portion of said path of travel, said sensing means including,

a light source positioned at one side of said loop,

a reflecting member positioned at the side of said loop opposite said light source in optical alignment therewith to receive radiation from said light source, and

a plurality of photosensitive devices disposed from said reflecting member in optical alignment therewith to receive radiation from said light source at predetermined lengths of said loop.

5. Apparatus for controlling the speed of one moving surface relative to another comprising,

an endless flexible member having a first portion thereof operatively associated with one of said moving surfaces to be driven at a surface speed proportional to that of said associated moving surface and a second portion thereof operatively associated with another of the moving surfaces to be driven at a surface speed proportional to that of said other associate moving surface,

means for forming a loop in said endless member along a third portion thereof between the as sociated portions of said moving surfaces, said loop being of a predetermined length-when the surface speed at which one of the moving surfaces is driven is at a predetermined level relative to the surface speed at which the other of the moving surfaces is driven,

means for sensing variations in the size of said loop from said predetermined length, said sensing means including,

a light source positioned at one side of said loop,

a reflecting member positioned at the side of said loop opposite said light source in optical alignment therewith to receive radiation from said light source, and

a plurality of photosensitive devices disposed from said reflecting member in optical alignment therewith to receive radiation from said light source at predetermined lengths of said loop.

6. Apparatus for controlling the surface speed of one endless xerographic plate relative to another in a duplex xerographic machine comprising,

an endless member having a first portion thereof operatively associated with one of said xerographic plates, to be driven at a speed proportional to said one of said xerographic plates,

said endless member having a second portion thereof operatively associated with another of said xerographic plates, to be driven at a speed proportional to said other of said xerographic plates,

said endless member having a third portion thereof formed into a loop, the length of which at any particular time period is dependent upon the relative speed at which said xerographic plates are moving, and

means operatively associated with the loop portion of said endless member for sensing variations in the length of said loop and for producing a corresponding change in the speed of at least one of said xerographic plates, said sensing means includmg,

a light source positioned at one side of said loop,

a reflecting member positioned at the side of said loop opposite said light source in optical alignment therewith to receive radiation from said light source, and

a plurality of photosensitive devices disposed from said reflecting member in optical alignment therewith to receive radiation from said light source at predetermined lengths of said loop.

7. Apparatus for controlling the surface speed of one endless xerographic plate relative to another in a duplex xerographic machine comprising,

an endless flexible member,

means defining a closed path of travel along which said endless member is driven including means alonga first portion thereof operatively associated with one of said xerographic plates for driving an associated portion of said endless member at a speed proportional to the speed at which said xerographic plate is driven, means along a second portion thereof operatively associated with the other of said xerographic plates for driving an associated portion of said endless member at a speed proportional to the speed at which said other xerographic plate is driven, and means along a third portion thereof for f rmin a loo 'n s id ndle member, means for sensing va riation in the size ofihe loop of said endless member along the third portion of said path of travel, said sensing means including,

a slight source positioned at one side of said loop,

a reflecting member positioned at the side of said loop opposite said light source in optical alignment therewith to receive radiation from said light source, and

a plurality of photosensitive devices disposed from said reflecting member in optical alignment therewith to receive radiation from said light source at predetermined lengths of said loop.

8. Apparatus for controlling the surface speed of one endless xerographic plate relative to another in a duplex xerographic machine comprising,

an endless flexible member having a first portion thereof operatively associated with one of said xerographic plates to be driven at a surface speed proportional to that of said xerographic plate and a second portion thereof operatively associated with another of the xerographic plates to be driven at a surface speed proportional to that of said other xerographic plate,

means for forming a loop in said endless member along a third portion thereof between the associated portions of said xerographic plates, said loop being of a predetermined length when the surface speed at which one of the xerographic plates is driven is at a predetermined level relative to the surface speed at which the other of the xerographic plates is driven,

means for sensing variations in the size of said loop from said predetermined length, said sensing means including,

a light source positioned at one side of said loop,

a reflecting member positioned at the side of said loop opposite said light source in optical alignment therewith to receive radiation from said light source, and

a plurality of photosensitive devices disposed from said reflecting member in optical alignment therewith to receive radiation from said light source at predetermined lengths of said loop. 

1. Apparatus for controlling the surface speed of one endless xErographic plate relative to another in a duplex xerographic machine comprising, an endless flexible member, means defining a closed path of travel along which said endless member is driven including means along a first portion thereof operatively associated with one of said xerographic plates for driving an associated portion of said endless member at a speed proportional to the speed at which said xerographic plate is driven, means along a second portion thereof operatively associated with the other of said xerographic plates for driving an associated portion of said endless member at a speed proportional to the speed at which said other xerographic plate is driven, and means along a third portion thereof for forming a loop in said endless member, means for sensing variations in the size of the loop of said endless member along the third portion of said path of travel including, a light source positioned at one side of said loop, a reflecting member positioned at the side of said loop opposite said light source in optical alignment therewith to receive radiation from said light source, and a plurality of photosensitive devices disposed from said reflecting member in optical alignment therewith to receive radiation from said light source at predetermined lengths of said loop, and drive means operatively associated with at least one of said xerographic plates and said plurality of photosensitive devices for controlling the speed at which at least one of said xerographic plates is driven.
 2. Apparatus for controlling the surface speed of one endless xerographic plate relative to another in a duplex xerographic machine comprising, an endless flexible member having a first portion thereof operatively associated with one of said xerographic plates to be driven at a surface speed proportional to that of said xerographic plate and a second portion thereof operatively associated with another of the xerographic plates to be driven at a surface speed proportional to that of said other xerographic plate, means for forming a loop in said endless member along a third portion thereof between the associated portions of said xerographic plates, said loop being of a predetermined length when the surface speed at which one of the xerographic plates is driven is at a predetermined level relative to the surface speed at which the other of the xerographic plates is driven, means for sensing variations in the size of said loop from said predetermined length including a light source positioned at one side of said loop, a reflecting member positioned at the side of said loop opposite said light source in optical alignment therewith to receive radiation from said light source, and a plurality of photosensitive devices disposed from said reflecting member in optical alignment therewith to receive radiation from said light source at predetermined lengths of said loop, and drive means operatively associated with at least one of said xerographic plates and said plurality of photosensitive devices for producing a correctional change in the relative speed at which at least one of said xerographic plates is driven in response to a variation in the size of said loop from said predetermined length.
 3. Apparatus for controlling the speed of one moving surface relative to another comprising, an endless member having a first portion thereof operatively associated with one of said moving surfaces, to be driven at a speed proportional to said one of said moving surfaces, said endless member having a second portion thereof operatively associated with another of said moving surfaces, to be driven at a speed proportional to said other of said moving surfaces, said endless member having a third portion thereof formed into a loop, the length of which at any particular time period is dependent upon the relative speed at which said surfaces are moving, means operatively associated with the loop portion of said endless member for sensing variations in the length of said loop and for producing a corresponding change in the speed of at least one of said moving surfaces, said sensing means including, a light source positioned at one side of said loop, a reflecting member positioned at the side of said loop opposite said light source in optical alignment therewith to receive radiation from said light source, and a plurality of photosensitive devices disposed from said reflecting member in optical alignment therewith to receive radiation from said light source at predetermined lengths of said loop.
 4. Apparatus for controlling the speed of one moving surface relative to another comprising, an endless flexible member, means defining a closed path of travel along which said endless member is driven including means along a first portion thereof operatively associated with one of said moving surfaces for driving an associated portion of said endless member at a speed proportional to the speed at which said moving surface is driven, means along a second portion thereof operatively associated with the other of said moving surfaces for driving an associated portion of said endless member at a speed proportional to the speed at which said other moving surface is driven, and means along a third portion thereof for forming a loop in said endless member, means for sensing variations in the size of the loop of said endless member along the third portion of said path of travel, said sensing means including, a light source positioned at one side of said loop, a reflecting member positioned at the side of said loop opposite said light source in optical alignment therewith to receive radiation from said light source, and a plurality of photosensitive devices disposed from said reflecting member in optical alignment therewith to receive radiation from said light source at predetermined lengths of said loop.
 5. Apparatus for controlling the speed of one moving surface relative to another comprising, an endless flexible member having a first portion thereof operatively associated with one of said moving surfaces to be driven at a surface speed proportional to that of said associated moving surface and a second portion thereof operatively associated with another of the moving surfaces to be driven at a surface speed proportional to that of said other associate moving surface, means for forming a loop in said endless member along a third portion thereof between the associated portions of said moving surfaces, said loop being of a predetermined length when the surface speed at which one of the moving surfaces is driven is at a predetermined level relative to the surface speed at which the other of the moving surfaces is driven, means for sensing variations in the size of said loop from said predetermined length, said sensing means including, a light source positioned at one side of said loop, a reflecting member positioned at the side of said loop opposite said light source in optical alignment therewith to receive radiation from said light source, and a plurality of photosensitive devices disposed from said reflecting member in optical alignment therewith to receive radiation from said light source at predetermined lengths of said loop.
 6. Apparatus for controlling the surface speed of one endless xerographic plate relative to another in a duplex xerographic machine comprising, an endless member having a first portion thereof operatively associated with one of said xerographic plates, to be driven at a speed proportional to said one of said xerographic plates, said endless member having a second portion thereof operatively associated with another of said xerographic plates, to be driven at a speed proportional to said other of said xerographic plates, said endless member having a third portion thereof formed into a loop, the length of which at any particular time period is dependent upon the relative speed at which said xerographic plates are moving, and Means operatively associated with the loop portion of said endless member for sensing variations in the length of said loop and for producing a corresponding change in the speed of at least one of said xerographic plates, said sensing means including, a light source positioned at one side of said loop, a reflecting member positioned at the side of said loop opposite said light source in optical alignment therewith to receive radiation from said light source, and a plurality of photosensitive devices disposed from said reflecting member in optical alignment therewith to receive radiation from said light source at predetermined lengths of said loop.
 7. Apparatus for controlling the surface speed of one endless xerographic plate relative to another in a duplex xerographic machine comprising, an endless flexible member, means defining a closed path of travel along which said endless member is driven including means along a first portion thereof operatively associated with one of said xerographic plates for driving an associated portion of said endless member at a speed proportional to the speed at which said xerographic plate is driven, means along a second portion thereof operatively associated with the other of said xerographic plates for driving an associated portion of said endless member at a speed proportional to the speed at which said other xerographic plate is driven, and means along a third portion thereof for forming a loop in said endless member, means for sensing variations in the size of the loop of said endless member along the third portion of said path of travel, said sensing means including, a slight source positioned at one side of said loop, a reflecting member positioned at the side of said loop opposite said light source in optical alignment therewith to receive radiation from said light source, and a plurality of photosensitive devices disposed from said reflecting member in optical alignment therewith to receive radiation from said light source at predetermined lengths of said loop.
 8. Apparatus for controlling the surface speed of one endless xerographic plate relative to another in a duplex xerographic machine comprising, an endless flexible member having a first portion thereof operatively associated with one of said xerographic plates to be driven at a surface speed proportional to that of said xerographic plate and a second portion thereof operatively associated with another of the xerographic plates to be driven at a surface speed proportional to that of said other xerographic plate, means for forming a loop in said endless member along a third portion thereof between the associated portions of said xerographic plates, said loop being of a predetermined length when the surface speed at which one of the xerographic plates is driven is at a predetermined level relative to the surface speed at which the other of the xerographic plates is driven, means for sensing variations in the size of said loop from said predetermined length, said sensing means including, a light source positioned at one side of said loop, a reflecting member positioned at the side of said loop opposite said light source in optical alignment therewith to receive radiation from said light source, and a plurality of photosensitive devices disposed from said reflecting member in optical alignment therewith to receive radiation from said light source at predetermined lengths of said loop. 